Clarify "Not on mobile" button text

Tester feedback has shown that desktop client users will also
click that button because they are, in fact, not on mobile.

This button speaks more to the users intent (sending the
invitation to the mobile device) after having (hopefully) read
the text above.

Fixes #38.

snikket_web/templates/invite_view.html

@@ -30,7 +30,7 @@
 {%- endif -%}
 		</ul>
 		{%- call standard_button("qrcode", "#qr-modal", class="primary", onclick="open_modal(this); return false;") -%}
-			{% trans %}Not on mobile?{% endtrans %}
+			{% trans %}Send to mobile device{% endtrans %}
 		{%- endcall -%}
 	</div>
 	<p>{% trans %}After installation the app should automatically open and prompt you to create an account. If not, simply click the button below.{% endtrans %}</p>